Although digital technology and innovative design have permeated the high-end audio niche for decades with CD players, SACD/DVD-A players, digital downloads, etc., amplification has remained largely analog. Strides in power supply efficiency have been made, but the heart of amplifiers still work as they have for years with varying twists on bipolar or MOSFET output.

Early digital amps were detailed and tightened up the bottom end, but were often characterized as sharp, harsh and edgy (full of ear grit as I would say). Over the last few years, however, great strides in digital amplifier technology have resulted in improved detail, bass speed and realism, but also smoothing out the grainy, hard edge of previous generations of digital amps.

One example of this new class of digital amplifiers is Rogue Audio’s Medusa. Who would have thought that a company that had exclusively designed traditional tube amps and preamps would come up with a digital/analog hybrid that is so breathtakingly accurate. Yet the amp is under $4,000 and still made-in-the USA.

Features

The Rogue Audio Medusa is a 200-wpc, hybrid digital amplifier, utilizing a tube input stage, three-stage analog power supply and a Class-D output stage utilizing Hypex digital modules with MOSFET output. According to chief designer and company president Mark O’Brien, the hybrid design offers the smoothness of tubes, but with the bass speed and accuracy of the best solid state.

O’Brien noted that he does not use the Class D modules as is, but the circuit is extensively modified to get the best sound possible. Much of the module is bypassed in favor of the custom, proprietary Rogue Audio design, he explained. The two 12AU7s hand-selected signal tubes serve as the phase inverter and internal front gain stages. O’Brien noted that three massive linear power supplies are used to power the amplifier circuitry and ultra-high quality parts are used extensively throughout the design. The Rogue Audio digital hybrid amps are available in two power configurations: the 100 watts per channel Hydra ($2,995) and the reviewed Medusa at 200 watts per channel ($3,995). They also come in black or the tinted silver finish that Rogue often uses. its hard to see the Rogue logo on the black version. The Medusa’s stereo input connection options include fully balanced XLR, or unbalanced single-end RCA, and the speaker outputs are five-way binding posts. An IEC power cord connection rounds out the back panel.

The
hybrid tube/Class D digital Rogue Audio Medusa is one of the best
amplifiers I have auditioned. It renders a very accurate soundstage with
tight bass and a very layered top end that matches or exceeds much more
expensive analog amps.

The front panel is simply the power switch and the standby/normal/fault operation LEDs. Overall, the look is quite attractive in its Rogue Audio, minimalist family resemblance. The anodized silver pigment hue is slightly darker than past Rogue products, but it looks and feels way more expensive than its list price would suggest. Although the amp is part digital, it is not a lightweight. It still weighs in at just under 40 pounds, with most of the heft in the power supplies and sturdy chassis. The manual is pretty basic and measured performance specs are sparse; only distortion and output power. No slew rate, damping factor or power draw numbers are cited.

The setup I installed the Rogue Audio Medusa in my main listening room. Speakers included Legacy Focus20/20s, Legacy Studios HDs, Paradigm Signature S8s and a set of Westlake Lc2.65 two-ways. I mated the Medusa with several preamps including my all-tube Rogue Audio 99 Magnum (6SN7 tubes), Pass Labs XP-10 MOSFET preamp, and my trusty Legacy/Coda high-current solid state output preamp. Source material was mostly high resolution and included music Blu-rays, DVD-As, SACDs, HD Tracks and ITRAX digital downloads, and my own 24-bit recordings of acoustic and jazz guitar. Players included the Oppo BDP-95universal player, and an Esoteric DV-50 DVD-A/SACD player.

Medusa's Digital Modules

To test my theory that the Medusa design would be superb for LP listening, I also listened to a number of high quality LPs via a Marantz TT-15 equipped with an Audio-Technica AT150ML cartridge, using the Pass Labs XP-15 phono preamp. All line and speaker connections were made using Alpha-Core Goertz silver cables. All components were plugged into the AC using an Essential Sound Products Essence power strip and Essence AC cables.
**After connection to the initial system, I let the Rogue burn in for three days and then commenced extensive listening sessions through the various sources and speaker options.

The audition As soon as I started listening to the Medusa through the Legacy Focus, I immediately noticed the tight bass. The bottom-end speed and precision made my reference Anthony Wilson Trio - Our Gang SACD sound extraordinary. On tube amps, the Legacys can be a bit plump, but the Rogue Medusa hybrid output projects this as clean as I’ve ever heard this jazz guitar/organ/drums recording. Yet the extension and fullness of the recording were there — like a well-setup live recording. Via the Medusa, the drum cymbals were unveiled — sharp, but not harsh, transient response that sounded natural with precise width and depth. When the bass is properly proportioned the treble and midrange are easier to wrap your ears around.

As I went through disc after disc and download after download, the Rogue never sounded thin or edgy. It is one of the few digital amps that I have liked (loved?) in my system. Even overly dense dance/pop music sounded damn good on this amp; usually, a no-no with traditional tube amps. Those of you who like your classical music through tube gear, will not be let down by the Medusa, in fact, the balanced sonic presentation will allow you to hear detail you may have never noticed — especially during the full power of a symphony. Violin harmonics, and the deep, yet tight wrapped tympani are much more life like on the Medusa than most tube amps I have owned or auditioned. A good example of this was the Popov - Symphony No. 1 Op. 7 - Leonard Botstein with the London Symphony Orchestra (Telarc). On either the Paradigms or the big Legacy Studios, when called for, this recording was conveyed with authority and sweetness. On my own live-to-stereo 24-bit PCM and DSD recordings played back through a TASCAM DVRA1000-HD professional deck, my Martin and Gibson guitar recordings were clear and concise, yet the width of the stereo image was deep and wide. The solid rosewood and spruce top acoustic guitar’s sonic signature was spot on — with that plucked presence you get from strumming new phosphor bronze strings. The Rogue Medusa is very natural sounding with acoustic instruments. Versus my $6,000 Bryston 14B-SST amp, the midbass seemed slightly tighter on the Rogue with the big Legacy Focus. On the smaller two-way speakers, the bass presentation was equal. The midrange and treble seemed more present with Rogue. But it did not sound edgy or harsh at all. (Maybe my 10-year old, heavily used Bryston is starting to show its age). Versus my all Class A Pass Labs XA30.5, the Rogue had a significantly leaner presentation, but I mean that in a good way. The Rogue’s bass again was so damn tight that it makes you think that other amps have a tone control turned up somewhere — especially with the generation two Focus speakers I use. Compared to the my reference Pass X350.5, priced at $13,000, the Medusa was similar in bass presentation, with maybe an edge in tightness when listening to the Legacy Focus. The Rogue was slightly more present in the treble, and the Pass supersymmetry MOSFET design seems to have a slightly less analytical presentation than the Medusa. The Pass’ stereo image is a bit larger and diffuse, while the Medusa’s image is precise and measured.

The Medusa’s ability to deliver deep, precise bass and clean, smooth (but accurate) mids and treble was showcased through all my speaker setups. The ribbon-tweeter based Legacy Studio never sounded better on the top-end. The Westlake LC2.65 and Paradigm 8s also were perfect mates for this amplifier, The Paradigm Signature S8’s beryllium tweeter transients are excellent with good amps, and the Medusa manages to transfer its midrange and treble presence through the Paradigms — without sounding exaggerated. One extra point of emphasis: vinyl-obsessed audiophiles will want to try this amp. The Medusa’s bass speed makes LP listening a more satisfying experience. Depending on cartridge used and that pesky RIAA curve, records can sound a bit thick (warmed, if you will) in the mid bass that gets re-thickened through preamps and low slew-rate analog amps; the Rogue does not impart any extra emphasis or sluggishness in the bass. Almost all the LPs I played via the Marantz TT-15 turntable, Pass XP-10 line preamp, XP-15 phono preamp and Rogue Medusa amp seemed more detailed and with less bass bloom. I had no problems with the Medusa — except when I stripped out a screw when putting the cover back on after my photo session with the amp’s internals). This build quality is typical of Rogue Audio ‘s hand-assembled quality. It never missed a beat. It ran warm, but never hot, and was quiet as a digital church mouse. In thinking about this amp as I wrote the review, the inevitability of digital amplifiers in the audiophile world came into clearer focus. The hybrid amps, and new generation of all-digital designs are going to become more plentiful; there is no stopping it. You already see digital amp technology used extensively on the professional side where smaller and energy efficient amps are made necessary because they are attached to speakers. And with digital amps like Rogue, the newer Bel Cantos and Pioneer’s new Elite class receivers entering the consumer fray, the market is destined for growth. If they sound as good as the Medusa, I am all for it. Definitely going to get a Medusa for my reference system.

The verdict

The hybrid tube/Class D digital Rogue Audio Medusa is one of the best amplifiers I have auditioned. It renders a very accurate soundstage with tight bass and a very layered top end that matches or exceeds much more expensive analog amps. It can drive most any speaker, and simply gets out of the way when playing the more revealing, high-resolution music. Combine the sound with less produced internal heat, longer component life and a very reasonable price tag for a high-end audiophile component, and the Medusa just might be the ideal, modernaudiophile amp. We are proud to give it a Stellar Sound Award.

The EAN Interview!

Rogue Audio Chief Talks About

New Digital Hybrid Amplifier

Editor’s Note: I have known Mark O'Brien since 1997, shortly after he created his small company, Rogue Audio. In that time, he has created a series of finely crafted, built-in-Pennsylvania tube amplifiers and preamplifiers. Breaking out of that traditional tube amp realm with the addition of the new Medusa hybrid amplifier, I recently conducted a brief Q/A session on his latest creation.

—John Gatski

EAN:As a tube amp designer, What made you want to design a digital amplifier?

MO: Class D amplifiers offer some significant benefits in terms of size, efficiency “green operation” and cost of ownership. Furthermore, the power tube maintenance associated with tube amplifiers can be a deterrent to ownership for some audiophiles. By combining the best of both worlds, I wanted to develop an amplifier that offered the sonic benefits of a large tube amp without any of the downsides. Essentially a compact, cool-running, yet powerful tube amp that an owner can just stick in a cabinet and forget about.EAN:What do you think the sonic benefits are of such a design?

MO: I think both of our new hybrids sound terrific and have excellent resolution as well as tremendous bottom end slam. They also provide tube smoothness without being overly euphonic. I really like the way they sound!

EAN:Can you gives a brief design run down on your design's circuit? Signal path components, etc.

MO: We use an OEM Class D module but bypass virtually everything on it except the modulator and MOSFET output section. All of the input and buffering is our own design and realized on our own circuit board. Generally speaking we use a proprietary input and intermediate stage that forces the output section to take on more of a tubelike sound quality. We also use large linear power supplies and very high quality parts to get lots of headroom and a very clean sound.

EAN:How does it differ from some of the other digital designs currently on the market, ICE, etc,.MO: During the development phase we built some pure Class D amps as a baseline, and they tended to sound pretty much the same. It took us awhile to get it just right, but when you bring tubes into the mix I believe it really brings the sound to another level.